The offset water knot is a knot used to join two ropes together. The offset water knot is formed by holding two rope ends next to each other and tying an overhand knot in them as if they were a single line. Due to its common use in several fields, this bend has become known by many names.

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Easily formed in most line, the offset water knot can be difficult or impossible to untie once tightened, if the knot's dressing has parts falling out of a neat, parallel ("twin") orientation.[1] Long used by weavers to join the ends of yarn, the offset water knot is very old. It was one of the knots likely identified among the possessions of Ötzi the Iceman, who dates from 3300 BC.[2] The knot is also tied in a slipped form by mechanical balers to bind straw and hay, but this bend is not practical to use as a binding knot when tied by hand.[3]

In rock climbing, the offset water knot is a favored knot for joining two ropes for a rappel longer than half the length of the ropes. (Although it can fail by capsizing under high loads, abseiling/rappelling doesn't generate such forces, and the knot, being on one side of the twin lines used in abseil, sees only half of this force.) American climbers, presumably believing the knot to be used only in hay bales or otherwise too vulnerable to flyping (inversion by capsizing), came to refer to it as the European Death Knot, abbreviated to EDK. But such capsizing is actually highly unlikely, and with the tails left long—and that is common advice—capsizing will likely make the knot tighter.[4]

Despite questions about this knot's security, it does present some advantages for use in rappels. Because the knot is offset from the axis of tension, it can slide more easily over rough surfaces than other knots; and it is quickly tied and readily untied. Along with its comparatively small size, this aids in rope retrieval by reducing its chance of getting stuck on edges, in cracks, or descent equipment. Since a stuck rope on a descent also represents a serious hazard to climbers, these advantages, along with ease of tying, have led to its popularity. It is recommended by some sources with the caveats that the ends be left very long (>30 cm), the knot be carefully dressed and fully tightened by pulling individually on all four strands, and then subjected only to moderate rappelling loads.[5]

The Offset Figure Eight Bend, a similar knot using the figure-eight knot, has been used in the belief that its greater size and complexity brings more security. But testing and more than one fatal failure indicate the figure-eight variant to be less secure, more prone to capsize at lower loads, and in capsizing uses more of the ends than does a capsizing overhand bend.[4][5] Moreover, while there is one obvious proper dressing of the Overhand Bend, there are a couple of dressings for the Offset Figure Eight Bend.[citation needed]